Data communication is becoming an important part of daily life. One of the most notable examples is the Internet, from which people receive electronic mail and visit web pages. Another example is in telephone communication. Many homes now own cordless phones that use digital spread spectrum technology to communicate digitized voice information between a cordless phone and a base station. Cellular phones also advanced from analog mode to digital operation. Recently, engineers envision that computers, home entertainment products, and home appliances will be linked together using a home-based local area network. Devices connected to this network may communicate with the outside world via the Internet. All these development rely on advances in digital data communication.
As more and more devices communicate digitally and more information is delivered through various networks, it is important to develop better ways to handle communication between all the devices. An important requirement is to increase the security of data communication. One of the most commonly used security measures is password. Passwords are very easy to use and convenient because no special equipment is required. However, it is known that systems relying on passwords are insecure. On the other hand, if a security measure is very cumbersome, people will not use it. Consequently, it is desirable to develop a simple to use way to enhance secure communicate between digital devices.